The prospect of explaining the Christian faith to pupils from faiths other than Christianity can seem daunting. However, this opportunity can arise at any time in school, e.g. through your contribution to an RE lesson, or in collective worship, an extracurricular activity or simply just in conversation. The resulting conversation can be incredibly rewarding; pupils from other faiths and cultures often understand the concept of religion being central to a person's life. It won't surprise them to hear you talk about God being all important to you, or that what you believe affects every area of your life.
Pupils and staff who are humanists or secularists, with no religious belief of their own, will have much less understanding of the importance of faith to a Christian than a believer from another religion.
Church members involved in schools aim to present Christianity in a genuine, positive and interesting way. You will need to remember that even if the differences between your Christian denomination and any other may be incredibly important to you, it is meaningless to most people who are not Christians. Stick to the essential beliefs of the Christian faith and don't confuse people with minor denominational differences unless they are genuinely interested and ask, or it is specified in the curriculum.
In conversations with people from different religions, it can help to look for areas of common interest between faiths. Asking about the role of Holy books in their faith is a good starting point, which leads on to an explanation about the importance of the Bible to Christians and how Christians believe that God speaks and guides them through the written words.
Similarly, discussions about festivals and places of worship can present good opportunities to explain the basics of Christianity in a stimulating way.
There are many website resources that can add further interest and insight about what it means to be a Christian.